SHELLS. 47 



are called, and you may apply these terms to 

 shells. 



Child. The point of the spire is then the apex, 

 and the part immediately opposite, the base. 



Teacher. You are right. 



Child. I think that when you described to us 

 how the shells were enlarged, you called the 

 opening the mouth. 



Teacher. Yes, it is termed either the mouth 

 or aperture. 



Child. Shells have also sides. 



Teacher. Yes, and it is necessary that you 

 learn to distinguish the two sides. You are sup- 

 posed, when you describe a shell, to place it upon 

 its base with its mouth turned towards you ; the 

 right side will then be that nearest to your right 

 hand, and the left that nearest your left hand. 



Child. What is the part turned toward me 

 called? 



Teacher. The front ; and what do you suppose 

 the reverse is ? 



Child. The back. 



Teacher. Look at this section of a shell.* 



Child. Is it cut down the middle that we may 

 observe the inside ? 



Teacher. Yes ; and what do you perceive ? 



Child. There is a pillar round which the 

 whorls appear to wind. 



Teacher. This pillar is called the Columella, 

 from the latin colum ella y a little column. 

 * See Section of a Shell. Plate I. 



